Henry E. (Henry Enfield) Roscoe.

A treatise on chemistry (Volume 3) online

. (page 36 of 50)
Online LibraryHenry E. (Henry Enfield) RoscoeA treatise on chemistry (Volume 3) → online text (page 36 of 50)
Font size
QR-code for this ebook


phenyl is easily oxidized to benzoic acid and that its derivatives
are completely different from those of xylol. 7

Glinzer and Fittig then undertook a careful examination of
methylbeuzyl, or, as they now termed it, methyltoluol ; like
xylol it yielded terephthalic acid on oxidation, but the trinitro-
derivatives proved to have different properties. 8 A further
investigation of the oxidation products of xylol showed that
toluic acid, the next homologue of benzoic acid, 9 is first formed,
and this was also obtained from methyltoluol. In spite of this,
however, the hydrocarbons were shown to be different, as the
properties of their substitution products did not agree. 10

Fittig and Velguth then obtained a third isomeric hydrocarbon,
which they named isoxylol, by heating monobasic mesitylenic
acid, C 6 H 3 (CH 3 ) 2 CO 2 H, prepared by the oxidation of mesitylene,






1 Ann. Chcm. Pharm. cxiii. 151. 2 Zcitschr. CJicm. 1864, 161.
3 Cumpt. Rend. lix. 47. * Ann. Chcm. Pharm. cxxxi. 303.

5 Ibid, cxxxiii. 32. 6 Ibid, cxxxiii. 47.

7 Ibid, cxxxiii. 222. 8 Ibid, cxxxvi. 303.

9 Yssel de Scheppcr and Beilstein, ibid, cxxxvii. 301.
10 Fittig, Ahreiisand Mattheides, ibid, cxlvii. 15.



388 AROMATIC COMPOUNDS

C 6 H 3 (CH 3 ) 3 , with lime. The substitution products of this body
agreed so exactly with those of xylol, that the two hydro-
carbons would have been considered identical had not their
oxidation products been completely different. Isoxylol was not
attacked by dilute nitric acid, while chromic acid oxidized it to
isophthalic acid, the isomeride of terephthalic acid. 1

Fittig soon found a very simple explanation of this exceptional
and almost incredible fact. Xylol proved to be a mixture* of
methyltoluol or paraxylol with isoxylol, or, as it is now termed,
metaxylol. Beilstein, who had looked upon it as a chemical
individual, had only obtained in a pure state the difficultly
soluble substitution products of metaxylol and the oxidation pro-
ducts of paraxylol, which are most readily formed. 2 The third
isomeric dimethylbenzene, orthoxylol was then prepared syn-
thetically and subsequently discovered in coal-tar by Jacobsen. 3

According to Fittig, coal-tar naphtha contains a preponde-
rating amount of metaxylene, while Jacobsen found 20 25 per
cent, of orthoxylene, and 10 15 per cent, of paraxylene in a
series of samples of xylerie.

In order to separate these, the coal-tar xylene, boiling at
about 140, is repeatedly shaken up with ordinary concentrated
sulphuric acid, the ortho- and meta-compounds alone being
dissolved. The solution is diluted with water and neutralized
with chalk, the filtrate being then treated with a slight excess
of sodium carbonate and concentrated by evaporation. The
sodium orthoxylenesulphonate separates out on cooling in large
prisms, which can readily be purified by re-crystallization.
An additional crop of this salt can be obtained by further eva-
poration, while the meta-salt remains in solution. The pure
hydrocarbons are then obtained by heating the salts with
concentrated hydrochloric acid.

The portion of the crude xylene which does not dissolve in
ordinary sulphuric is agitated with the slightly fuming acid,
the mixture being gently heated; the paraffins are thus left
undissolved, while paraxylenesulphonic acid is formed, which
is only slightly soluble in dilute sulphuric acid, and is purified
by re-crystallization (Jacobsen), the hydrocarbon being then
obtained, as before, by the action of hydrochloric acid.

The meta-compound alone may be extracted from crude
xylene by boiling it for a considerable time with a mixture of

1 Ann. Chem. Pharm. cxlviii. 1. 2 Ibid, cliii. 265.

3 Ber. Deutsch. Chem. Ges. x. 1010,



THE XYLENES 389






one volume of concentrated nitric acid and two or three volumes
of water, the ortho- and para-compounds being thus oxidized to
the corresponding toluic acids, C e H 4 (CH 3 )CO 2 H, or their nitro-
derivatives, while the meta-compound is scarcely attacked.
When the evolution of red fumes ceases, the liquid is distilled
with steam and the distillate agitated with caustic soda, washed
with water, dried and distilled. 1

In order to estimate the amounts of the three isomerides
quantitatively, 100 c.c. of the crude xylene are boiled for half
an hour to an hour with a mixture of 40 c.c. of nitric acid
of sp. gr. 1*4 and 60 c.c. of water, the whole being repeatedly
agitated. The unattacked portion is then washed with caustic
soda and distilled with steam, the distillate is measured and
shaken up with 1*5 vols. of concentrated sulphuric acid, the
metaxylene being thus dissolved, while the paraffins remain
behind and are measured in a graduated cylinder.

The amount of paraxylene is found by thoroughly agitating
100 c.c. of the crude xylene with 120 c.c. of concentrated sul-
phuric acid for half an hour, a mixture of paraffins and para-
xylene being left undissolved ; this is then treated with an
equal volume of fuming sulphuric acid, containing 20 per cent,
of trioxide, which dissolves out the paraxylene. The amounts
of paraxylene, metaxylene and paraffins are thus directly
measured, the difference from 100 c.c. being that of the
orthoxylene.

In this way Levinstein has found in various samples of crude
English and Scotch xylene : 2

Paraxylene 3 10 per cent.

Metaxylene 7087

Orthoxylene 215

Paraffins . , 310

According to Renter these methods of separation are not accurate,
since nitric acid of the concentration employed also attacks
metaxylene, and paraxylene dissolves in ordinary sulphuric acid,
although to a much smaller extent than its isomerides. The
resistance of the xylenes to the action of a.cids is, however,
considerably increased by the presence of paraffins. 3

1 Fittig and Voljruth, Ann. Chcm. Pharm. cxlviii. 10 ; Tawildarow, Zcitschr.
Chcm. 1870, 418 ; Bruckner, Bcr. Dcutech. Chcm. Ges. ix. 405.

2 Ibid. xvii. 444. 3 ^id. xvii. 2028.



390 AROMATIC COMPOUNDS.

When a mixture of the three xylenes is treated with bromine
containing 1 per cent, of iodine, they are converted into the tetra-
bromoxylenes, C 6 Br 4 (CH 3 ) 2 , which yield the tetrabromoplithalic
acids quantitatively when heated with bromine and water to
160 170 :

C 6 Br 4 (OH 3 ) 2 + 6Br 2 + 4H 2 = C 6 Br,(CO 2 H) 2 + 1 2HBr.

Since these can readily be separated, the composition of the
original mixture can be determined in this way. 1



THE XYLENES, OR DIMETHYLBENZENES,

C 6 H 4 (CH 3 ) 2 .

2209 Orthoxylene, (1 : 2), was first prepared pure by the dis-
tillation of paraxylic acid, C 6 H 3 (CH 3 ) 2 CO 2 H, with lime ; 2 it is
also formed by the action of sodium on a mixture of ortho-
bromotoluene and methyl iodide, 3 and when a hot mixture of
toluene and aluminium chloride is treated with methyl chloride.
A small quantity of paraxylene is always formed in this reaction,
together with still less metaxylene and a larger amount of
the isomeric trimethylbenzenes. 4 It has also been prepared
from cantharidin, C 10 H 12 O 4 , which is the characteristic con-
stituent of Spanish flies, and yields pure orthoxylene when
heated with phosphorus pentasulphide. 5

It is a liquid which boils at 142 143, solidifies in a freezing
mixture to crystals, melting at 28, 6 and is oxidized to ortho-
toluic acid by heating with dilute nitric acid, while chromic
acid produces complete combustion. When agitated with a
boiling solution of potassium permanganate, however, it yields
phthalic acid. 7 A cold mixture of nitric and sulphuric acids
converts it into liquid nitro-derivatives, and a single drop of
orthoxylene can thus be distinguished from the para- and
meta-compounds. 8

Friedel and Crafts, Compt. rend. ci. 1218.

Bieber and Fittig, Ann. Chcm. Pharm. clvi. 238.

Hiibner and Jannasch, ibid. clxx. 117 ; Reymann, Hull. Soe. Chim. xxvi. 532.

Jacobsen, Rer. Dcutsch. Chcm. Gcs. xiv. 2624.

Piccard, ibid. xii. 580.

Colson, Ann. Chim. Phys. [6] vi. 128.

Glaus and Pieszcek, Bcr. Dcutsch. Ch&n. Gcs. xix. 3083.

Jacobsen, ibid. xix. 2518.



ORTHOXYLENE. 391



IHkydro-orthoxylene, or Cantharene, C 6 H 6 (CH 3 ) 2 . The com-
pound C ]0 H 12 I O 3 is formed by the action of hydriodic acid on
cantharidin, and is converted into cantharene by heating with
concentrated caustic potash ; the latter boils at 134, smells like
camphor and oil of turpentine, rapidly absorbs oxygen from the
air and is oxidized to orthotoluic acid by dilute nitric acid. 1

Metaxylene (1 : 3) may be obtained pure by heating xylic acid
C fi H 3 (CH 3 ) 2 CO 2 H (Bieber and Fittig), or the isomeric mesity-
lenic acid (Fittig and Velguth) with lime, and by the action of
sodium on a mixture of methyl iodide and meta-iodotoluene. 2
It boils at 139-8 and has a specific gravity of 0-8780 at 0, and of
8GCO at 15 ; it solidifies when strongly cooled and then melts
at - 54 to -53. 3 It is only attacked with difficulty by dilute
nitric acid, even on boiling ; when, however, it is boiled for
several hours with nitric acid of specific gravity 1'4, diluted
with one and a half times its volume of water, metatoluic acid is
obtained (Reuter), while chromic acid solution oxidizes it to
isophthalic acid, which is also formed, together with metatoluic
acid, by the action of potassium permanganate. 4

Metaxylene, as already mentioned, occurs in various tars and
petroleums, and it has also been found in that from the
Caucasus. 5 It forms a characteristic trinitro-derivative, which is
only slightly soluble in alcohol and yields nitrodiamidometaxy-
Icne (p. 409) on partial reduction. These reactions serve to
detect small quantities of metaxylene in petroleum, &c.

Tetraliydromelaxylene, C 6 H 8 (CH 3 ). 2 , is formed when camphoric
acid, C 8 H 14 (C0 2 H) 2> is heated to 200 with concentrated hydriodic
acid, 6 and has also been prepared from oxycamphoric acid, under
which it will be mentioned. It is a liquid which boils at 119,
and is converted into trinitrometaxylene by a mixture of nitric
and sulphuric acids.

HcxJiydrometaxykne, C e H 10 (CH 3 ) 2 , is obtained by heating
camphoric acid or metaxylene with hydriodic acid to 280. It
occurs in Baku petroleum (Beilstein and Kurbatow) and in
essence of resin (Renard) ; it boils at 116 120, and also yields
trinitrometaxylene with nitric and sulphuric acids. 7

Paraxyknc (1:4) is formed by the action of sodium on a

1 Piccard, Bcr. Dcntsch. Chcm. Gcs. xix. 1406.

2 Wroblewsky, Ann. Chcm. Pharm. cxcii. 200. 3 Colson, loc. oil.

4 Clans and Hurst ert, Btr. Dcntech. Chc.m. Gc*. xix. 3084.

5 Doroschenko, xviii. Ref. 662 ; Markownikow, Ann. Clicm. rhann. ccxxxiv.
89.

6 Wrcden, Ann. Clum. Pharm. clxxxvii. 171. 7 Ibid, clxxxvii. 151.



AROMATIC COMPOUNDS.



mixture of methyl iodide and parabromotoluene l or paradi-
bromobenzene. 2 It boils at 136 137, and has a specific gravity
of O8621 atl9'5; when strongly cooled it solidifies to rhombic
prisms resembling heavy spar, 3 which melt at + 15. Dilute
nitric acid oxidizes it to paratoluic acid, while chromic acid or
potassium permanganate give terephthalic acid.

Paraxylene occurs in the petroleum from Galicia along with
metaxylene. 4

Hexhydroparaxylene, C C H 10 (CH 3 ) 2 , is obtained by heating mono-
bromocamphor, C 10 H 15 BrO, with zinc chloride to 150 160, and
is a liquid boiling at 157 '6, which is converted into trinitropara-
xylene by nitric and sulphuric acids. 5



SUBSTITUTION PRODUCTS OF THE XYLENES.

2210 When one atom of hydrogen is replaced in the aromatic
nucleus, six isomeric compounds may be formed. Metaxylene
yields three, which are distinguished as symmetric = s, asym-
metric = a, and adjacent (vicinus) = v. Two, asymmetric = a,
and adjacent = v, are derived from orthoxylene, while paraxylene
only yields one, which has therefore received no more particular
designation.



HALOGEN SUBSTITUTION PRODUCTS OF THE
XYLENES.

v-Ohlororthosaylene, C 6 H 3 (CH 3 ) 2 C1(1 : 2 : 3), is formed, together
with the following compound, when orthoxylene, to which 5 per
cent, of iodine has been added, is treated with chlorine at 0. In
order to separate the two isomerides, they are converted into the
sulphonic acids, the pure sodium salts of which are then
decomposed by heating with concentrated hydrochloric acid.
Adjacent chlororthoxylene is a liquid boiling at ISO'S .

a-Chlororthoxyhne (1:2:4) boils at 191-5 and, like its
isomeride, remains liquid at 20. 6

1 Fittig and Glinzer, Ann. Chcm. Pharm. cxxxvi. 303.
V. Meyer, Ber. Deutsch. Chcm. Gcs. iii. 753 ; Jannasch, ibid. x. 1356.
3 Jacobsen, ibid. xvii. 2379. 4 Pawlewski, ibid, xviii. 1915.

5 R. Schiff, ibid. xiii. 1408. 6 Kriiger. ibid, xviii. 1755.



XYLENE SUBSTITUTION-PRODUCTS. 393

The chlororthoxylenes are converted by oxidation into the
corresponding chlorotoluic and chlorophthalic acids.

According to Glaus and Kautz, only one chlororthoxylene is
formed, which boils at 205 and yields the following compounds
on further chlorination : l

Melting- Boiling-

Dichlororthoxylene, C 6 H 2 C1. 2 (CH 3 ).,, point. point.

crystalline mass . . . . + 3 227
Trichlororthoxylene, C 6 HC1 3 (CH 3 ) 2 ,

lustrous needles .... 93 265
Tetrachlororthoxylene, C/J1 4 (CH 3 ) 2 ,

long needles . . ... . 215

a-Chlorometaxylene, C 6 H 3 (CH 3 \C1(1 : 3 : 4), is formed when
metaxylene is chlorinated at in presence of iodine ; the crude
product, which distils between 185 188, is purified by con-
verting it into the sulphonic acid and then preparing the sodium
salt or chloromeiaxylenesutpkamide, C 6 H 2 (S0 2 .ISIH 2 )C1(CH 3 ) 2 ,
from this. The latter crystallizes from hot alcohol in hard, com-
pact, lustrous prisms melting at 195T Both of these compounds
yield pure chlorometaxylene when heated with hydrochloric acid.
It boils at 186'5 and does not solidify at - 20 ; it is oxidized to
chlorometatoluic acid by chromic acid, while it is converted
into ortho-homoparahydroxybenzoic acid by fusion with caustic
potash. 2

Ckloroparaxylene, C 6 H 3 (CH 3 ) 2 C1(1 : 4 : 2), is obtained in a
precisely similar manner to chlorometaxylene ; it boils at 186
and solidifies in a freezing mixture to a crystalline mass, which
melts at + 2.

Dicliloroparaxykne, C 6 H 2 (CH 3 ) 2 C1 2 , is only slightly soluble in
cold, readily in hot alcohol, and crystallizes in flat needles or
plates ; it melts at 71 and boils at 221 . 3

a-Bromorthoxylcne, C 6 H 3 (CH 3 \Br(l : 2 : 4), is formed by the
direct bromination of orthoxylene in the cold in the presence of
iodine, no isomeride being produced, 4 and more slowly when
bromine alone is allowed to act in the dark, orthoxylyl bromide
being obtained in the sunlight 5 It boils at 214'5 and solidifies
below to a fibrous, crystalline mass, melting at 0'2. When
heated with ethyl ehlorofoimate and sodium amalgam, paraxylic
acid, C ( .H 3 (CH 3 ) 2 CO 2 H, is formed.

1 Jacobsen, Bcr. DcutseJi. Chcm. Gcs. xviii. 1367.

- Ibid, xviii. 1760. 3 Kluge, ibid, xviii. 2098.

4 Jacobsen, ibid. xvii. 2372. 5 Schramm, ibid, xviii. 1278.



394 AROMATIC COMPOUNDS.

The following compounds are formed by the further action of
bromine (Jacobsen) :

^oliddibromorthoxylcnc,C e H.. 2 (C'H. s } 2 Br. 2 (l : 2 :4 : 5), crystallizes
from hot alcohol in large, rhombic plates, which melt at 88 ; it
readily sublimes in very large, thin plates, boils at 278 and yields
symmetric tetramethylbenzene, C G H 2 (CH 3 ) 4 , on treatment with
sodium and methyl iodide.

Liquid dibromorthoxylene boils at 277 and solidifies in the
cold to a hard crystalline mass, melting at + 6'8.

Tetralromorthcxyknc, C 6 (CH 3 ) 2 Br 4 , is formed when orthoxylene
is allowed to drop into bromine containing 1 per cent, of alumi-
nium bromide, the whole being kept at 0. 1 It is very slightly
soluble in alcohol, readily in benzene, and crystallizes in long,
lustrous needles, which melt at 262, or according to Bliimlein at
254 255, and boil at 374 375.

Jacobsen was unable to prepare tribromorthoxylene pure.

a-Bromomctaxylcnc., C 6 H 3 (CH 3 ) 2 Br (1 :3:4), is prepared like
the ortho-compound ; it is a liquid, which boils at 203 204-,
and is converted into the corresponding bromotoluic acid by oxi-
dation, 2 while xylic acid is formed by the action of carbon
dioxide and sodium. 3

s-Bromometaxylcne, (1:3: 5), has been prepared from bromi-
nated metaxylidine by the diazo-reaction. It boils at 20-i ,
remains liquid at 20, and is converted into symmetric
dimethylethylbenzene by sodium and ethyl bromide. 4

a-Dibromcmdaxylcnc, C 6 H 2 (CH 3 ) 2 Br. 2 , is formed when meta-
xylene is allowed to stand in contact with an excess of bromine
for twenty-four hours, the liquid being kept cool. 5 It crystallizes
from alcohol in colourless, nacreous plates, boils at 255 250,
and melts at 72. 6

P-Dibromomdaxylene was obtained by Wroblewsky, together
with his monobromoxylene, as a liquid which boils at 252 and
does not solidify at 20.

Tctrabromomctaxylcne, C ( .(CH 3 ) 2 Br 4 , is formed when meta-
xylene is allowed to stand for a long time in contact with
a large excess of bromine. It is scarcely soluble in cold,
slightly in boiling alcohol, but dissolves readily in benzene,

Bliimlein, Ber. Dcutsch. Chcm Gcs. xvii. 2492.

Fittig, Ann. Clicm. Pharm. cxlvii. 31.

Kekule, ibid, cxxxvii. 186.

WroWewsky, ibid, cxcii. 115.

Fittig, Ahrens and Mattheides, ibid, cxlvii. 24.

Fittig and Bieber, ibid. clvi. 236.






NITRO-ORTIIOXYLENES. 395

and crystallizes in fine needles which melt at 241 (Fittig
and Bieber).

Bromoparaxylene, C 6 H 3 (CH 3 ) 2 Br (1:4: 2), is prepared by the
action of bromine on cooled paraxylene in the presence of iodine,
and is also formed when bromine is allowed to act alone in the
dark (Schramm). It is a liquid, which boils at 205'5, and some-
times solidifies when strongly cooled, but frequently remains
liquid until a crystal of the solid compound has been added, when
it forms plates or tablets, melting at + 9. 1

Dibromoparaxylene, C 6 H 2 (CH 3 ) 2 Br 2 (1:4:2:5), boils at 261,
and crystallizes from alcohol in large plates or flat needles,
melting at 75 '5. When these are allowed to remain in the
mother liquor they are converted into transparent, asymmetric
crystals, which closely resemble regular octohedra (Jacobsen).
It is converted into symmetric tetramethylbenzene by the action
of sodium and methyl iodide. 2

In addition to this compound, a liquid dibromoparaxylene,
which boils at 260 264 and solidifies in a freezing mixture,
is formed in small quantity.

A tribromoparaxylene was not formed when the necessary
quantity of bromine was added, the following substance being
obtained together with the preceding compounds :

Tetrabromoparaxylcne, C 6 (CH 3 ) 2 Br 4 , is very slightly soluble in
alcohol, and crystallizes from hot toluene in long, fine needles,
melting at 253.



NITRO-SUBSTITUTION PRODUCTS OF THE
XYLENES.

2211 v-Nitro-orthoxylcnc, C C H 3 (CH 3 ) 2 NO 2 (1:2: 3), is formed,
together with the following compound, when orthoxylene is
treated in a freezing mixture with concentrated nitric and
sulphuric acids ; it is a liquid, which boils at 245 247 . 3

a-Nitro-orthoxylene (1 : 2 : 4) is almost the sole product when
pure nitric acid is employed ; it crystallizes from alcohol in long,
brittle, light yellow, lustrous prisms, melts at 290 and boils at
280 4

1 Jannasch, Ann. Chem. Pliarm. clxxi. 82 ; Jacohscn, Bcr. Dmtsck. Clitm.
Gcs. xviii. 356. u Jannasch, ibid. x. 1357.

3 Nblting and Forcl, ibid, xviii. 2669. 4 Ibid. xvii. 159.



3!)6 AROMATIC COMPOUNDS.



Dinitro-orihoxylcne, C 6 H 2 (CH 3 ) 2 (NO 2 ) 2 , is formed, together
with the following compound when orthoxylene is heated for
a considerable time to 100 with a mixture of nitric and sul-
phuric acids. It crystallizes from boiling alcohol in long, lustrous
needles, melting at 71.

Trinitro-orthoxyhnc, C 6 H(CH 3 ) 2 (NO 2 ) 3 , forms white, lustrous
scales, which melt at 178, and are almost insoluble in
alcohol. 1

v-Nitrometaxylene (1:3:2) is obtained by the action of nitric
and sulphuric acids on metaxylene in the cold. 2 It has been
prepared pure from the corresponding nitrometaxylidine by the
diazo-reaction. 3 It is a liquid boiling at 225.

a-Nilrometaxylene (1:3:4) is formed in the preparation of
the preceding compound, and in preponderating amount when
pure, well-cooled nitric acid is employed. It is a light yellow
liquid, which boils at 238 and does not solidify at - 20. 4

s-Nitromeiaxylcne (1:3:5) is obtained from nitro-a-metaxy-
lidine by dissolving it in absolute alcohol, adding two molecules
of sulphuric acid, and then treating the well-cooled liquid with
twice the theoretical quantity of ethyl nitrite in order to prevent
the formation of the diazo-amido-compound. The liquid is
heated to boiling after standing for some time, the alcohol driven
off and the remainder distilled with steam.

s-Nitromdaxylenc boils at 263, and crystallizes from alcohol
in large, flat needles, melting at 74 75. 5

s-IJinilrometaxyhne, C 6 H 2 (CH 3 ) 2 (NO 2 ) 2 (1 : 3 : 4 : 6), is readily
prepared by heating metaxylene with fuming nitric acid ; it
crystallizes from hot alcohol in large, flat, colourless needles or
lustrous prisms, melting at 93. 6

v-Dinitrometaxylene (1:3:4:2) is formed together with its
isomerides when xylene is nitrated at a low temperature with
a mixture of nitric and sulphuric acids ; it is readily soluble in
alcohol, and crystallizes in scale-like plates, melting at 83. 7

Trinitrometaxylene, C 6 H(CH 3 ) 2 (NO 2 ) 3 (1:3:2:4:6). This
characteristic compound, which has been previously mentioned

Drossbach. Bcr. Dculsch. Chcm. Ges. xix. 2156.

Nolting and Forel, Bcr. Deutsch. Chem. Ges. xviii. 2668.

Grevingk, ibid. xvii. 2430.

Tawildarow, Zeitschr. Chcm. 1870, 418 ; Harmsen, Bcr Dcutsch.Chem. Ges.
. 1558.

Wroblewsky, Ann. Chem. Pharm. ccvii. 91 ; Thol, Ber. Deutsch. Chem. Ges.
ii. 359 ; .Nolting and Forel.

Fittig, Ann. Chem. Pharm. cxlvii. 16 ; cxlviii. 5.

Grevingk, Ber. Deutsch. Chcm. Ges. xvii. 2422.



XITROXYLENES. 397

(p. 387), is formed when rnetaxylene or the preceding compounds
are heated with a mixture of nitric and sulphuric acids. It
is scarcely soluble in cold, very slightly in boiling alcohol,
and crystallizes in fine, flat, colourless needles, melting at
176 . 1

Nitroparaxylene, C 6 H 3 (CH 3 ) 2 N0 2 , is obtained by allowing the
calculated quantity of fuming nitric acid to drop into well-cooled
paraxylene. It is a yellow liquid, which toils at 239 and does
not solidfy at - 20. 2

a-Dinitroparaxylene, C 6 H 2 (CH 3 ) 2 (NO 2 ) 2 (1 : 4 : 2 : 6), is formed,
together with its isomerides, when paraxylene is dissolved in
cold, fuming nitric acid. It crystallizes from alcohol in very thin,
lustrous needles, melting at. 124, and is deposited from glacial
acetic acid in long, broad needles.

ft-Linitroparaxylene (1:4:2:3) is more readily soluble in
alcohol, and crystallizes on gradual evaporation in monoclinic
tablets, which resemble crystals of calcspar, and melt at 93. 3
It is a characteristic property of these two nitroxylenes that
equal molecules of them combine to form a double compound,
which can be crystallized from glacial acetic acid, but is de-
composed by alcohol into its constituents. 4 It forms transparent
monoclinic prisms with sphenoid faces, and melts at 99'5.

fy-Dinitroparaxylene (1:4:2:5) is slightly soluble in cold,
more readily in hot alcohol, and forms long, yellow needles with
a vitreous lustre, which melt at 147 148 . 5

Lellmann determined the constitutions of these three isomerides
by the methods already described (Part III., p. 245) ; the first
two, which are formed in largest quantity, were converted into
the hydrochlorides of the corresponding diamines, their solutions
evaporated with ammonium thiocyanate, and the residues heated
to 120, ground up with water, washed, dissolved in caustic soda,
and these solutions heated with lead acetate. The a- compound
gave a precipitate of lead sulphide while the /S-compound did
not, and was thus proved to be an orthodiamine.

He then prepared the free a-diamidoparaxylene, which is a
crystalline mass, and combines with allyl mustard oil to form the
compound C 6 H 2 (CH 3 ) 2 (NH.CS.NH.C 3 H 5 ) 2 , which crystallizes in

1 Luhraann, Ann. Chcm. Pharm. cxliv. 276 ; Fittig, loc. cit. ; Grevingk, loc cit.

2 Jannasch, Ann. Chcm. Pharm. clxxvi. 55 ; Nblting and Forel, loc. cit.

3 Fittig and Glinzer, Ann. Chcm. Pharm. cxxxvi. 307 ; Fittig, Ahrens and
Mattheides, ibid, cxlvii. 17.

4 Jannasch and Stiinkel, Bcr. Deutsch. Chem. Ges. xiv. 1146.

5 Lellmann, Ann. Chcm. Pharm. ccxxviii. 250.



398 AROMATIC COMPOUNDS.



small needles, melting without decomposition at 112'5. It is



Online LibraryHenry E. (Henry Enfield) RoscoeA treatise on chemistry (Volume 3) → online text (page 36 of 50)